The invention relates to an apparatus for the pasting of plastic films, preferably for the affixing of section of plastic film to flat-lying workpieces made of plastic film, e.g. of valve sections to the applied bottom squares or of bottom covers to the added bottoms of cross bottom valve sacks, consisting of a rack with a plate or a table over which the tube parts or workpieces are continuously transported by a conveyor unit, of a conveyor roller pair disposed in a gap in the table top and supported in the rack whose roller gap is essentially flush with the table surface and whose lower roller is a counter-pressure roller and whose upper roller is a suction cylinder, of a conveyor cylinder interacting with the suction cylinder which successively transfers the sections to the suction cylinder and of a broad-slit nozzle directed to the roller gap which blows heated air into the roller gap in a controlled manner.
In an apparatus of this type known from DE 195 02 255 A1, the workpieces, that is, for example in the manufacture of cross bottom sacks, the tube pieces with applied or added bottoms, are continually transported over a plate or a table on which they are supported, with them sliding over the table. If sections or covers are applied simultaneously to both applied or added bottoms, the successive transportation of the workpieces is performed in a transverse orientation. The table is provided with a conveyor roller pair in a gap whose roller gap is essentially flush with the table surface so that the workpieces can run into this roller gap. Of the conveyor roller pair, the lower roller is designed as the counter-pressure roller while the upper roller is a suction cylinder. This suction cylinder, which has air-intake boreholes provided in its jacket, for example at equal angle distances, works together with a conveyor cylinder which successively transfers the sections to the suction cylinder. This suction cylinder thus irons--so to speak--the sections in the roller gap on the workpieces running therethrough. So that the section adheres to the workpiece, a broad-slit nozzle is directed onto the roller gap which blows heated air into the roller gap in a controlled manner. In this process, the air possesses such a high temperature that the surfaces of the section and of the workpiece are plasticised up to stickiness so that the sections are pressed onto the workpiece in the roller gap of the conveyor roller pair and in this way a good adhesion of the section to the workpiece is performed. The feed of the sections is coordinated with the passage of the workpieces in such a way that a positionally correct pasting of the sections to the workpieces is performed. The feed of the hot air in this process is controlled in such a way that essentially only the regions to be pasted together are plasticised or fused in the required manner. In this process, the rate of passage of the individual workpiece and the section are selected so that a good adhesion of both parts is performed. As the hot air which effects the adhesion is blown into the roller gap, it cannot be excluded that the suction cylinder heats up as time passes. This warming is, however, basically of a non-damaging nature, as the suction cylinder has no mechanical parts, for example gripping devices, which could become incapable of function over the operating time due to clogging with plasticised plastic. If necessary, the suction roller can additionally be provided with a cooling. In any case, the suction roller prevents the conveyor cylinder from heating up in an impermissible manner due to the hot air so that its functional capability could be impaired.
The adhesion of the sections to be pasted to the upper roller of the conveyor roller pair could also be effected by the upper roller comprising a statically charged cylinder instead of a suction cylinder.
The conveyor cylinder transferring the sections to the suction cylinder is appropriately a cutter cylinder whose cutters separate the sections from a plastic sheet running continuously or intermittently. To retain the section on the conveyor cylinder, it can be wrapped on a part of its circumference by a strand side of an endless belt or an endless belt herd which press the section to be transferred to the circumference of the conveyor cylinder.
The conveyor cylinder can also be provided with grips to retain the sections on it.
Appropriately a cooling sheet is disposed above the table top, with the workpieces being fed to the roller gap through the gap between the cooling sheet and the table top. This cooling sheet, which can be provided with channels through which a cooling medium flow, prevents the table and other apparatus parts from heating up due to the hot air blown into the roller gap in such a way that the workpieces in plastic become sticky and may get caught on the table top or other apparatus parts.
In another aspect of the invention, there is disposed in the feed line to the broad-slit nozzle a valve which is provided with a control device for the controlled blowing out of the hot air into the roller gap. The valve can, for example, consist of a rotary slide valve which is adjusted by a pressure means piston cylinder unit for its control.
To focus the broad-slit nozzle in an optimum manner on the roller gap, the broad-slit nozzle can be travelled by a control device in the direction of the roller gap and back.
In this process, the broad-slit nozzle can be travelled back so far that it is completely removed from the region of the roller gap.
One special problem in the apparatus known from DE 195 02 255 A1 results from the fact that the required quantity of heat has to be supplied to the regions to be pasted by the heated air blown out of the broad-slit nozzle. This quantity of heat, however, fluctuates in accordance with the ambient temperature and the temperature of the apparatus. For this reason, in the known device, the heating unit which warms the air is connected to an adjustment apparatus which the machine operator adjusts on the basis of his observation of the pasted regions in such a way that hotter or colder air is blown out from the broad-slit nozzle. The adjustment of the temperature of the heated air by hand on the basis of an observation of the pasted regions is, however, necessarily subject to error as both the observations can not be performed precisely enough and because the adjustment by hand cannot be effected precisely enough.